I. Field of the Invention
This invention relates to sealed bearing rotary cone drill bits and a means to prevent debris from entering the bearings.
More particularly, this invention provides a spring loaded shale burn plug between a leg back face and a rotary cone to divert debris away from the seal, seal cavity and bearings.
II. Description of the Prior Art
It has long been recognized in the drill bit industry that the longevity of sealed bearing rotary cone drill bits is greatly increased if debris is prevented from entering the bearings associated with each of the rotary cones rotatively retained on legs of a drill bit. Drill bits used in carrying out rotary drilling have been subject to destruction by erosion caused by the abrasive effect of the materials present in the drilling method. Fluid circulation is employed primarily to circulate or flush the debris or cuttings from the well bore. In actual practice, mud and solids from the circulating fluid and from the earthen formation pack onto certain portions of the bit structure and this pack material flows or extrudes and moves relative to certain portions of the bit. Since great pressures are utilized in the drilling operations, the movement or flow of this pack material has adverse effects on the bit structure and, in particular, the seal cavity, seal and bearings associated with each rotary cone of the bit.
U.S. Pat. No. 2,960,313 addresses the foregoing problem. A means is provided to mechanically deflect mud and fluid material from a path that normally results in wear and destruction of a roller bit. A deflecting post or pin is provided in a leg back face. The end of the pin is adjacent a cone back face; the pin serving to deflect detritus or debris as it invades the space between the cone back face and the leg back face. The pin is fixed in the leg back face and has an exposed cylindrical end that terminates in a flat surface, the flat surface paralleling the rotary cone back face.
The deflecting post, while it is somewhat effective in intercepting the flow of debris, its circular shape can divert debris and fluid towards a seal cavity thus allowing some debris to enter this cavity.
U.S. Pat. No. 3,013,621 describes a means to deflect abrasive particles or cuttings from the space formed between a leg back face and a conical cutter. An overlay of hardened materials is welded to the leg back face at an angle to a radial plane extending from a journal center line. The abrasive material metallurgically attached to the leg back face serves to scrape or divert debris away from rotary cone bearings to prevent the debris from destroying the bearing during operation of the bit in a borehole.
The raised hardened material applied to the leg back face is less effective when the cone axially oscillates (on its journal) away from the leg back face during operation of the bit in a borehole.
The present invention has an advantage over both of these prior art mechanisms int hat the debris deflecting device is spring loaded so that the shale burn plug face remains in constant contact with the cone back face thereby providing a more reliable and effective means to deflect the debris away from the seal cavities during operation of the drill bit in a borehole.
Moreover, the shale burn plug is provided with a raised ridge in the face of the energized shale burn plug to more effectively divert debris from the seal cavity associated with each of the rotary cones.